Spectrum generator



se ts, 1957 Filed July 22, 1955 J. J. HUPERT ET AL SPECTRUM GENERATOR 5Shets-Sheet 1 13 I w w I l l I 20 MC RESONANT REACTANCE CRYSTAL 20 Mc-TUBE I OSCILLATOR STAGE CIRCUIT I I 22325 1 1 i5 71' OSCILLATOR I I I 1i v J2 J l 1 RESONANT I 22!- IO MC STAGE I l l l i I GENERATOR 1 l l 1 5MC I 1 CRYSTAL I A OSCILLOSCOPE I OSCILLATOR 73 l x l l I f I I l I IRESONANT SWEPT 2 MC 626 FREQUENCY STAGE OSCILLATOR I I A l l SAW-T T 1MC RESONANT 32 SS H I z I I CRYSTAL 40o KC I OSCILLATOR I OSCILLATORCIRCUIT l I I 26 15 I l l 200 KC CRYSTAL I I OSCILLATOR 1 L INVENTORS.JZZZZZJS' If fizz 092% Josef; 1 5'. zazbef daf y Sept. 3, 1957 J. J.HUPERT ETAL SPECTRUM GENERATOR 3 Sheets-Sheet 2 Filed July 22, 1955INVENTORS per? fi J 4 Sept. 3, 1957 J- J. HUPERT ET AL SPECTRUMGENERATOR Filed July 22, 1955 I5 Sheets-Sheet 5 PER/OD OF -4OO KC- B/ASL/ NE SHADED PORTIONS REPRESENT PARKS OF THE GRID VOLTAGE UT/L/ZEDFORTf/E EXC/TAT/O/V OF THE CURRENT FLOW IN THE NEXT STAGE -PER/00 OF 200KC PER/0D 0F 2M0 10 MC STAGE B/AS LINE PER/0D OF 20 MC MAJOR PATTERNREPEATED AT 200 KC RATE MIXER BIAS L/NE PERIOD OF 200 KC INVENTORS.

mia i :5 17 2 g MfZ Z United States l atentecl Sept. 3, 1957 liceSPECTRUM GENERATQR Julius ll. Hupert, Glen Ellyn, and Joseph S. Nabcr,Wheeling, 111., assignors to A. R. F. Products, Inc., River Forest,111., a corporation of Illinois Application July 22, 1955, Serial No.523,638

12 Claims. (Cl. 250-46) The present invention relates to electricalsignal generators and in particular to signal generators for producingequally spaced signals throughout a region of the electromagneticspectrum.

It is often desirable to calibrate a variable frequency oscillator. Theoscillator may be successively beat against a number of the signalsproduced by a spectrum generator and the position of the frequencyvarying means noted. Since the frequency of the oscillator is usuallyknown to be within a frequency range and the frequency of each of thespectral signals is known to be integrally related to the lowestfrequency signal produced by the signal generator, each of the beatsoccurs at a known frequency.

Spectrum generators may produce a single pulse containing frequencycomponents extending up to the high frequency end of the spectrum underconsideration, or a spectrum generator may produce a plurality ofintegrally related signals of different frequency.

it is necessary that the spectral signals extend to the upper frequencylimit of the variable oscillator in order to employ this method offrequency calibration. As an example, it is conventional to employ 200kilocycle oscillators to generate spectral signals extending up toapproximately 20 megacycles. However, if it is desired to generatespectral signals spaced by the same frequency interval to a much higherfrequency, for example 400 megacyclcs, a simple oscillator can not beemployed. It is thus an object of the present invention to provide aspectrum ge crating device which will produce spectral signals separatedby narrow intervals throughout a larger range of the electromagneticspectrum.

in general, the interval between adjacent spectral signals need not beas small for higher portions of a spectrum than for lower portions ofthe spectrum. Further, it is sometimes difiicult to identify thefrequency of a given spectrum signal if the spectral signals are atclose intervals. It is therefore a further object of the presentinvention to provide a spectrum generator which will generate spectralsignals covering a wide frequency spectrum having means for selectingthe interval between adjacent spectral signals.

The inventors achieve the above objects by generating pulses in a tunedcircuit having a resonant frequency somewhere in the spectrum to begenerated above the lowest frequency spectral signal to be generated.The frequency of resonance of the tuned circuit is chosen to produce apulse which contains a sufficient spectral distribution to reach theupper end of the spectrum which is to be generated. The tank circuit isconnected in a class C stage, and the stage is driven by pulses havingthe desired repetition rate to produce the proper interval betweenadjacent spectral signals. The driving pulses for the class C stagecontaining the resonant circuit must themselves be relatively short, andthese pulses may readily be generated by driving the driving stage forthe class C amplifier with pulses which are produced in resonant tankcircuits of lower frequency than the driving stage. By cascading aseries of stages operating in this manner the ultimate spectral intervalcan be obtained from the lowest driving frequency. It is also necessarythat each of the driving stages contain tank circuits with resonantfrequencies which are integrally related in order to generate theharmonic of the pulse impressed upon a given stage from its drivingstage.

When a pulse is impressed upon a resonant tank circuit which has aresonant frequency which is integrally related to the fundamentalfrequency of the pulses, so that the pulse contains a harmonic at theresonant frequency of the tank circuit, a damped wave train occurshaving the frequency of resonance of the tank circuit. If this wavetrain is used further to drive a succeeding stage and the succeedingstage is biased to cut off all but the initial pulse of the wave train,it is clear that the pulse width from the succeeding stage will be shortrelative to degrees in that stage. if in a spectrum generatorconstructed to carry out this method of operation, each of the drivingstages is biased to respond only to the first pulse of the damped wavetrain of the preceding stage, the shape of the wave appearing at theoutput of the last stage will itself be a damped wave train of the samefrequency as the frequency of resonance of the final class C stage.However, if the biases on some of the stages in the spectrum generatorare not properly set so that each stage responds to a larger portion ofthe Wave than the first pulse in the damped wave train, then a complexwave form will appear at the output of the last stage, and this complexwave will have a repetition rate equal to the frequency of the firstdriving stage in the spectrum generator.

As a result of the complex wave form appearing in the resonant circuitof the final stage of the spectrum generator, some of the spectralsignals in restricted portions of the generated spectrum will tend tocancel, or partially cancel. This is undesirable, particularly if theoutput of the spectrum generator is to be impressed upon anoscilloscope. it is therefore a further object of the present inventionto provide a spectrum generator which produces a spectrum by the methodoutlined above which avoids partial cancellation of spectral signals inrestricted portions of the generated spectrum.

These and other objects of the present invention will be more readilyunderstood from a further reading of the present disclosure,particularly when viewed in the light of the drawings, in which:

Figure l is a block diagram of a spectrum generating device constructedaccording to the teachings of the present invention;

Figure 2 is a schematic electrical diagram of the spectrum generator,mixer, and indicating means illustrated in Figure 1;

Figure 3 is a graph showing the relationship between time and theinstantaneous value of the current appearing in the plate circuit of the460 kilocycle stage of the spectrum generating device;

Figure 4 is a graph showing the relationship between time and theinstantaneous value of the current appearing in the plate circuit of the2 niegacycle stage of the spectrum generating device; and

Figure 5 is a graph showing the relationship between time and theinstantaneous value of the current appearing in the plate circuit of the20 megacycle stage of the spectrum generating device.

As illustrated in Figure 1, a manually tuned variable frequencyoscillator 18, which is to be calibrated by heating the output of theoscillator against a number of signals from a spectrum generatingdevice, designated 13, is connected to the input. of the mixer 12.Theoutput of a spectrum generating device 13, constructed according tothe teachings of the present invention, is also connected to the inputof the mixer 12, and the output of the mixer 12 is connected toanindicating means, such as an audio reproducer which will indicate zerobeat between the oscillator and one of the spectral signals from thespectrum generating device 13, or an oscilloscope, designated 14, havinga saw-tooth sweep oscillator 16 connected thereto. The saw-toothoscillator 16 is also connected to a swept frequency oscillator 17 andfrequency modulates the swept frequency oscillator 17 synchronously withthe oscilloscope horizontal sweep. The swept frequency oscillator 17 iscoupled to the mixer 12 in order to provide frequency markers on theoscilloscope 14.

The spectrum generator 13 has a 20 megacycle resonant stage 18 whichgenerates the spectral signals and operates in all cases, and theresonant stage 18 is coupled to the input of the mixer 12. When thespectral lines are to be generator 13 which are in operation under thisparticular set of conditions.

In the event that a 5 megacycle separation between spectral frequencies,or lines, is desired, the 20 megacycle crystal oscillator 20 isdeactuated, and a 5 megacycle crystal oscillator 22 is energized. The 5megacycle crystal oscillator 22 is coupled to the input of the 20megacycle resonant stage 18 through a 10 megacycle stage 24, which isalso energized. Under these conditions, the 5 megacycle crystaloscillator produces pulses in the form of damped wave trains in theoutput circuits of the 10 megacycle stage 24 and 20 megacycle stage 18,and these pulses have a repetition rate of 5 megacycles. In this manner,pulses having the shape of the 20 megacycle stage 18, and hence desiredspectral distribution, are produced with a repetition rate of 5megacycles.

In like manner, a l megacycle separation between spectral lines may beobtained by actuating a 1 megacycle crystal oscillator 26 anddeactuating the 5 megacycle crystal oscillator 22 and 20 megacyclecrystal oscillator 20. The 1 megacycle crystal oscillator 26 is coupledto the input of the resonant 1O megacycle stage 24 through a resonant 2megacycle stage 28, which is also energized.

Also, a spectral line separation of 200 kilocycles may be obtained inthe same manner by actuating a 200 kilocycle crystal oscillator 30 and aresonant 400 kilocycle circuit 32, and deactuating the crystaloscillators 20, 22 and 26.

The schematic electrical circuit diagram for the spectrum generator,mixer, and a portion of the oscilloscope appears in Figure 2. Since theoscilloscope 14 and sweep oscillator 16 are conventional, their circuitshave not been shown. The mixer 12 utilizes a vacuum tube 34 in aconventional mixing circuit, the variable frequency oscillator 10 beingconnected to the control grid 36 of the vacuum 34 through a condenser38. The control grid 36 is connected to the negative terminal of asuitable power source, such as battery 48, through a resistor 42. Thecathode 44, or return electrode, of vacuum tube 34 is also connected tothe negative terminal of power source 40 through a resistor 46. Theplate 48 of vacuum tube 34 is connected to the positive terminal of thepower source 40 through a plate resistor 50. The output signal from theresonant 20 megacycle stage 18 is connected to the cathode 44 of vacuumtube 34 through a condenser 52.

The 20 megacycle resonant stage 18 is a class C amplifier and has avacuum tube 54 with a plate 56 connected to a parallel resonant tankcircuit 58 through a coupling condenser 57 and to the positive terminalof the power source 40 through a radio frequency choke 59. The other endof the tank circuit 58 is connected to the negative terminal of thepower source 40. Vacuum tube 54 also has a control grid 60 which iscoupled to the 20 megacycle crystal oscillator 20 and to the resonant 10megacycle stage 24 through a coupling condenser 62. The cathode 64 ofvacuum tube 54 is connected to the negative terminal of the power source40, and the screen grid 66 of vacuum tube 54 is connected to thepositive terminal of the power source 40 through a dropping resistor 68,the screen grid also being by-passed to the negative terminal of thepower source 40 by condenser 76. The tank circuit 58 of the resonantZOmegacycle stage 18 is tuned to resonant at 20 rnegacycles.

The resonant frequency of the tank circuit 58 is periodically varied bya reactance tube circuit 71 connected in parallel with the tank circuit58, and a sinusoidal oscillator 73, connected to the reactance tubecircuit 71. The reactance tube circuit 71 has a vacuum tube 75 with aplate 77 connected to the plate end of the tank circuit 58 through acondenser 79. The cathode 81 of vacuum tube 75 is connected to the otherend of the tank circuit 58, and a resistor 87 is connected in serieswith a condenser 89 and connected in parallel with the tank circuit 58.Vacuum tube 75 also has a control grid 91 which is connected to thejunction of resistor 87 and condenser 89 through a condenser 93. Thealternating current generator 73 is connected between the control grid91 of vacuum tube 75 and the cathode 81 thereof in series with aresistor 95 and a negative grid bias supply, such as battery 101. Asource of voltage, such as the 'battery 40, is connected between thecathode 81 and the plate 77 of vacuum tube 75, through a choke 10-3.Vaciuum tube 75 also has a screen grid 105 which is connected to thepositive terminal of battery 40 through a resistor 107 and to thenegative terminal of battery 40 through a by-pass condenser 109. Vacuumtube 75 also has a suppressor grid 111 which is connected to a cathode81 thereof.

The 20 megacycle crystal oscillator 20 uses a vacuum 'tube 72 with acathode 74 which is coupled into the through a resistor 83 and switch84, and the plate 82 is also by-passed to the negative terminal of thepower source by a condenser 85. The cathode 74 of the 20 megacyclecrystal oscillator 20 is also connected to the negative terminal of thepower source 40 through a tank circuit 88 which includes a coil 90connected in parallel with the condenser 92. The tank circuit 88 is nottuned to the resonant frequency of the crystal 78, but to a frequencylower than the resonant frequency of the crystal 78. In the particularconstruction, the tank circuit 88 is tuned to a frequency of 10megacycles, where the resonant frequency of the crystal 78 is 20megacycles. Hence at the frequency of 20 megacycles, the tank circuit 88merely presents, a reactance to the circuit.

The 5 megacycle crystal oscillator 22 is constructed in a manner similarto the 20 megacycle crystal oscillator 20. The 5 megacycle crystaloscillator 22 has a vacuum tube 94 with a plate 96 connected to thepositive terminal 'of the'powe'r source 40 through "a resistor 97 andswitch 98. Vacuum tube 94 also has a grid 1% connected to 'the negativeterminal of the power source 4% through a crystal 102 connected inparallel with a resistor 184, the crystal 102 having a resonantfrequency of 5 megacycles. Vacuum tube 94 also has a cathode 106connected to the negative terminal of the power cource through a tankcircuit 108 having a resonant frequency below that of the resonantfrequency of the crystal 102, in the particular construction theresonant frequency being 2 megacycles. The plate 96 of vacuum tube 94 isalso by-passed to the negative terminal of the power source 40 bycondenser 109.

The 5 megacycle signal produced by the 5 megacycle oscillator 22 iscoupled to the input of the 20 megacycle resonant stage through themegacycle resonant stage 24. The 10 megacycle resonant stage 24 has avacuum tube 110 with a control grid 112 which is coupled to the cathod106 of tube 94 of the 5 megacycle oscillator through a condenser 114.The grid is also connected to the negative terminal of the power sourcethrough a grid resistor 116. The cathode 118 of vacuum tube 110 is alsoconnected to the negative terminal of the power source 40. The vacuumtube 110 has a plate 120 which is coupled through a coupling condenser122 to the cathode 74 of vacuum tube 72. In addition, vacuum tube 110has a screen grid 126 connected to the positive terminal of the powersource 40 through a resistor 128 and to the negative terminal of thepower source through a by-pass condenser 130. The plate 120 of vacuumtube 110 is also connected to the positive terminal of the power sourcethrough a plate resistor 132 connected in series with a switch 134.

The 1 megacycle crystal oscillator 26 is also of similar construction tothe 20 megacycle oscillator 20. It has "a vacuum tube 136 with a grid138 connected to the negative terminal of the power source 40 throughparallel connected resistor 140 and crystal 142, the resonant frequencyof the crystal 142 being 1 megacycle. Vacuum tube 136 also has a plate144 which is connected to the positive terminal of the power source 40through a resistor 145 and switch 146 and to the negative terminal ofthe power source 40 through a by-pass condenser 148. Vacuum tube 136 hasa cathode, or return electrode 150, which is connected to a tank circuit152 having a parallelly connected coil 154 and condenser 156, theopposite end of the tank circuit 152 being connected to the negativeterminal of the power shource 40. The resonant frequency of the tankcircuit 152 in the particular construction is 400 kilocycles, where theresonant frequency of the crystal is 1 megacycle.

The l mega-cycle crystal oscillator 26 is coupled to the 10 megacycleresonant stage 24 through a 2 megacycle resonant stage 28. The 2megacycle resonant stage 23 has a vacuum tube 158 with a control grid160 coupled to the cathode 150 of vacuum tube 136 through a condenser162. Vacuum tube 158 also has a cathode 164 connected to the negativeterminal of the power source, and the grid 1611 of vacuum tube 158 isalso connected to the negative terminal of the power source through agrid resistor 1 66. Vacuum tube 153 also has a screen grit. 17bconnected to the positive terminal of the power source through aresistor 172 and to the negative terminal of the power source through acondenser 174. Vacuum tube 158 is also provided with a plate 176 whichis coupled to the cathode 106 of the 5 megacycle oscillator 22 through acoupling condenser 178, the plate 176 also being connected to thepositive terminal of the power source 4-0 through a plate resistor 180and a switch 182 connected in series. it is to be noted, that the tankcircuit serves both as an impedance for the 5 megacycle crystaloscillator and as a resonant tank circuit for the resonant 2 megacyclestage 28.

The 200 kilocycle oscillator 30 is coupled through condenser 184 to thecathode 150 of the l megacycle crystal oscillator 26. It utilizes twotubes 136 and 1558 connected in an oscillator circuit, a 200 kilocyclecrystal 190 being connected between the grid 192 of vacuum tube 188 andthe plate of vacuum tube 136. The cathodes 196 of vacuum tube 188 and198 of vacuum tube 186 are in erconnected and connected to the negativeterminal of the power source 40 through a resistor 200. The grid 192 ofvacuum tube 188 is also connected to the cathodes 196 and 198 through aresistor 202. The grid 204 of vacuum tube 186 is directly connected tothe negative terminal of the power source. Vacuum tube 188 has a plate206 which is connected to the positive terminal of the power source 40through a switch 208, and the the plate 206 is connected to the negativeterminal of the power source 40 through a by-pass condenser 210. Theplate 194 of vacuum tube 186 is also connected to the positive terminalof the power source through resistor 212 and the switch 213 connected inseries.

In order to produce a spectrum with a 20 megacycle separation betweenadjacent spectral signals, only switch 84 of the 20 megacycle crystaloscillator 20 is closed, the other switches 98, 134, 146, 182, 208 and213 being open. A 5 megacycle separation between spectrum signals isobtained with switches 84, 146, 182, 208 and 213 open, and switches 98and 134 close. A l megacycle separation between adjacent spectralsignals is obtained by opening switches 84, 93, 208 and 214 and closingswitches 146, 182 and 134. Finally, a spectrum with a 200 kilocycleseparation between adjacent spectral signals is obtained with switches208, 214, 182 and 134 closed, and switches 146, 98 and 84 open.

The operation of the spectrum generator is best illustrated wthen theswitches are positioned as last indicated in order to produce a spectrumwith a 200 kilocycle separation between adjacent spectral signals. Underthese conditions the 200 kilocycle oscillator 30 is producin anessential sinusoidal wave having a frequency of 200 kilocycles persecond and impressing this wave upon the 400 kilocycle tank circuit 32.The current flowing in the 406 kilocycle tank circuit 32 takes the formillustrated in Figure 3 of the drawings. It will be noted that alternatepeaks of the wave, designated 214, are of smaller amplitude than theother peaks, these smaller peaks being derived from the second harmonicof the wave produced by the oscillator The input circuit of the resonant2 megacycle stage 28 is biased to respond only to the larger peaks,designated 216, appearing across the tank circuit 32, the negative biaslevel being indicated by the dashed line 218 in Figure 3 and beingprovided by the grid resistor 166 in the resonant 2 megacycle stage 28.As a result, the grid of vacuum tube 158 in the 2 megacycle resonantstage 23 is driven by a pulse which is narrow compared with degrees atthe frequency of 400 kilocycles per second and has a repetition rate of200 kilocycles per second.

The current appearing in the plate circuit of the 2 megacycle stage 28is illustrated in Figure 4 of the drawings. It will be noted, that thelarger pulses 216 which are impressed upon the input of the 2 megacycleresonant stage 28 produce a damped wave in the plate current of the 2megacycle stage 28 with a resonant frequency equal to that of the tankcircuit 108, namely 2 megacycles. it will also be noted, that thesmaller pulses 214 which are impressed upon the grid 160 of the 2megacycle stage 238 produce relatively small variations in the platecurrent of vacuum tube 158. It will also be noted that the initialpulse, designated 220, of each damped wave train appearing in the tankcircuit 108 is of substantially higher amplitude than the followingpulse 222; and further has a wave form which is narrow compared with 180degrees at a frequency of 2 megacycles. The grid 112 of vacuum tube 110of the resonant 10 megacycle stage 24 is negatively biased to excludeall but the initial pulse 220 of each wave train appearing in the tankcircuit 108, the level of this bias being indicated by the dashed line224 in Figure 4. In this manner, the initial pulse 220 produces a dampedwave train having a resonant frequency of 10 megacycles in the tankcircuit 88 of the 10 mega cycle resonant stage 24. The grid 60 of thevacuum tube of the 20 megacycle resonant stage 18 is also negativelybiased to respond only to the initial pulse of the damped wave trainappearing in the tank circuit 88, thus producing a wave in the form of adamped wave train having a frequency of -20 megacycles in the tankcircuit 58 of the resonant-20 megacycle stage 18, this Wave beingillustrated in Figure 5. Again, the negative bias indicated by thedashed line 226 in Figure is applied to the grid 36 of the mixer tube34, so that only the initial pulse 228 of the damped wave trainappearing in the tank circuit 58 effects the plate current of the mixerstage 12.

From the foregoing analysis, it is clear that a negative 7 grid bias inany one of the resonant stages 18, 24, 28 and 32 which is notsufficiently negative will cause the stage to respond to both theinitial pulse of the damped wave train and the succeeding pulse. Underthese conditions, the pulse appearing in the tank circuit 58 and the 20megacycle resonant stage will not take the form illustrated in Figure 5,but rather will be a complex wave. The spectral components of such acomplex wave will produce cancellations in localized regions of thegenerated spectrum.

' The inventors have found, however, that the deleterious effects ofthese cancellations can be substantially elimnated by varying theresonant frequency of the tank circuit 58, or one of the precedingamplifier stages 24 or 28, to shift the region of cancellation from aregion of interest to a region of no interest. The effect of shiftingthe resonant frequency of tank circuit 58 is to vary the time intervalbetween the initial pulse 228 of the damped wave train appearing thereinand the succeeding pulse, since this interval is a function of thefrequency of resonance of the tank circuit 58. The initial pulse 228,however, is essentially undisturbed. As a result, the region ofcancellation of the spectral signals is shifted. The reactance tubecircuit 71 connected in parallel with the tank circuit 58 accomplishesthis function. The bias placed upon the grid 91 of the reactance tube 75is varied in order to shift the regions of cancellation. The problem ofpartial cancellations is essentially eliminated, by impressing asinusoidal bias voltage upon a grid 91 of the reactance tube 75. Thesignal generator 73 connected in the grid bias circuit accomplishes thispurpose.

The foregoing disclosure is directed to a specific embodiment of thepresent invention. t is clearly within the skill of the art to devisemodifications to the foregoing embodiment and other embodiments withinthe skill of the art. For example, many conventional means of frequencymodulation may be employed to vary the resonant frequency of the tankcircuit of the resonant output stage of the spectrum generator, such asa motor driven variable condenser. It is therefore intended that thescope of the present invention be not limited by the foregoingdisclosure, but rather only by the appended claims.

The invention claimed is:

1. An electrical device comprising an oscillator having a resonantfrequency, a first non-oscillating harmonic selector having an inputcircuit coupled to the oscillator and a resonant output circuit having afrequency of resonance an integral multiple above the resonant frequencyof the oscillator in which a damped wave train is produced, and a secondnon-oscillating harmonic selector having an input circuit coupled to theoutput circuit of the first harmonic selector and a resonant outputcircuit having a frequency of resonance an integral multiple above thefrequency of resonance of the output circuit of the first harmonicselector, said second harmonic selector including means for rejecting aportion of each wave train impressed thereon to form a hiatus betweensuccessive Wave trains.

2. An electrical device comprising an oscillator having a resonantfrequency, a first non-oscillating harmonic selector having an inputcircuit coupled to the oscillator and a resonant output circuit having afrequency of resonance an integral multiple above the resonant frequency of the oscillator in which a damped Wave train is produced, asecond non-oscillating harmonic selector having an input circuit coupledto the output circuit of the first harmonic selector and a resonantoutput circuit having a frequency of resonance an integral multipleabove the frequency of resonance of theoutput circuit of the firstharmonic selector, said second harmonic selector including means forrejecting a portion of each wave train impressed thereon to form ahiatus between successive wave trains, and means to vary the resonantfrequency of the output circuit of the second harmonic selector.

3. An electrical device comprising an oscillator having aresonantfrequency, a first non-oscillating harmonic selector having aninput circuit coupled to the oscillator and a resonant output circuithaving a frequency of resonance an integral multiple above the resonantfrequency of the oscillator in which a damped wave train is produced, asecond non-oscillating harmonic selector having an input circuit coupledto the output circuit of the first harmonic selector and a resonantoutput circuit having a frequency of resonance an integral multipleabove the frequency of resonance of the output circuit of the firstharmonic selector, said second harmonic selector including means forrejecting pulses with amplitudes no greater than a threshold value, anda reactance tube circuit connected in parallel with the resonant outputcircuit of the second harmonic selector.

4. An electrical device comprising an oscillator having a resonantfrequency, a first non-oscillating harmonic selector having an inputcircuit coupled to the oscillator and a resonant output circuit having afrequency of resonance-an integral multiple above the resonant frequencyof the oscillator in which a damped wave train is produced, a secondnon-oscillating harmonic selector having an input circuit coupled to theoutput circuit of the first harmonic selector and a resonant outputcircuit having a frequency of resonance an integral multiple above thefrequency of resonance of the output circuit of the first harmonicselector, said second harmonic selector including means for rejectingpulses with amplitudes no greater than the second pulse of the dampedwave train in the output circuit of the first harmonic selector, areactance tub'e circuit connected in parallel with the resonant outputcircuit of the second harmonic selector, and an alternating currentsource of voltage connected to the reactance tube circuit toperiodically vary the resonant frequency of the output circuit of thesecond harmonic selector.

5. An electrical device comprising an oscillator having a fixed resonantfrequency, a first non-oscillating class C stage having a vacuum tube,said stage having an input circuit connected between the grid and returnelectrode of said vacuum tube coupled to the oscillator and an outputcircuit connected between the plate and return electrode of said vacuumtube, including a tank circuit having a resonant frequency which is anintegral multiple above the resonant frequency of the oscillator inwhich a damped wave train is produced, and a second class C stage havinga vacuum tube, 'said stage having an input circuit connected between thegrid and return electrode of the vacuum tube in said second class Cstage, said input circuit being coupled to the output circuit of thefirst class C stage, said second class C stage having an output circuithaving a tank circuit with a frequency of resonance which is an integralmultiple of the resonant frequency of the tank circuit in the firststage, and said second class C stage including means to negatively biasthe grid of the vacuum tube to reject pulses with amplitudes no greaterthan the second pulse of the damped wave train in the output circuit ofthe first harmonic selector.

6. An electrical device comprising an oscillator having a fixed resonantfrequency, a first non-oscillating class C stage having a vacuum tube,said stage having an input circuit connected between the grid and returnelectrode of said vacuum tube coupled to the oscillator and an outputcircuit connected between the plate and return electrode of said vacuumtube including a tank circuit having a resonant frequency which is anintegral multiple above the resonant frequency of the oscillator inwhich a damped wave train is produced, a second class C stage having avacuum tube, said stage having an input circuit connected between thegrid and return electrode of the vacuum tube in said second class Cstage, said input circuit being coupled to the output circuit of thefirst class C stage, said second class C stage having an output circuithaving a tank circuit with a frequency of resonance which is an integralmultiple of the resonant frequency of the tank circuit in the firststage, and said second class C stage including means to negatively biasthe grid of the vacuum tube to reject pulses with amplitudes no greaterthan the second pulse of the damped wave train in the output circuit ofthe first harmonic selector, and means to vary the resonant frequency ofthe tank circuit in the output circuit of the second class C stage.

7. An electrical device comprising an oscillator having a fixed resonantfrequency, a first non-oscillating class C stage having a vacuum tube,said stage having an input circuit connected between the grid and returnelectrode of said vacuum tube coupled to the oscillator and an outputcircuit connected between the plate and return electrode of said vacuumtube including a tank circuit having a resonant frequency which is anintegral multiple above the resonant frequency of the oscillator inwhich a damped wave train is produced, and a second class C stage havinga vacuum tube, said stage having an input circuit connected between thegrid and return electrode of the vacuum tube in said second class Cstage, said input circuit being coupled to the output circuit of thefirst class C stage, said second class C stage having an output circuithaving a tank circuit including a variable condenser and coil with afrequency of resonance which is an integral multiple of the resonantfrequency of the tank circuit in the first stage, and said second classC stage including means to negatively bias the grid of the vacuum tubeto reject pulses with amplitudes no greater than the second pulse of thedamped wave train in the output circuit of the first harmonic selector.

8. An electrical device comprising an oscillator having a fixed resonantfrequency, a first non-oscillating class C stage having a vacuum tube,said stage having an input circuit connected between the grid and returnelectrode of said vacuum tube coupled to the oscillator and an outputcircuit connected between the plate and return electrode of said vacuumtube, including a tank circuit having a resonant frequency which is anintegral multiple above the resonant frequency of the oscillator inwhich a damped wave train is produced, a second class C stage having avacuum tube, said stage having an input circuit connected between thegrid and return electrode of the vacuum tube in said second class Cstage, said input circuit being coupled to the output circuit of thefirst class C stage, said second class C stage having an output circuithaving a tank circuit with a frequency of resonance which is an integralmultiple of the resonant frequency of the tank circuit in the firststage, and said second class C stage including means to negatively biasthe grid of the vacuum tube to reject pulses with amplitudes no greaterthan the second pulse of the damped Wave train in the output circuit ofthe first harmonic selector, and a reactance tube circuit connected inparallel with the tank circuit of the second class C stage.

9. An electrical device comprising an oscillator having a fixed resonantfrequency, a first non-oscillating class C stage having a vacuum tube,said stage having an input circuit connected between the grid and returnelectrode of said vacuum tube coupled to the oscillator and an outputcircuit connected between the plate and return electrode of said vacuumtube, including a tank circuit having a resonant frequency which is anintegral multiple above the resonant frequency of the oscillator inwhich a damped Wave train is produced, a second class C stage having avacuum tube, said stage having an input circuit connected between thegrid and return electrode of the vacuum tube in said second class Cstage, said input cir= cuit being coupled to the output circuit of thefirst class C stage, said second class C stage having an output circuithaving a tank circuit with a frequency of resonance which is an integralmultiple of the resonant frequency of the tank circuit in the firststage, and said second class C stage including means to negatively biasthe grid of the vacuum tube to reject pulses with amplitudes no greaterthan the second pulse of the damped wave train in the output circuit ofthe first harmonic selector, a reactance tube circuit connected inparallel with the tank circuit of the second class C stage, and analternating current generator connected to the reactance tube circuit toperiodically vary the resonant frequency of the tank circuit in thesecond class C stage.

10. An electrical device comprising an oscillator having a resonantfrequency, a first non-oscillating harmonic selector having an inputcircuit coupled to the oscillator and a resonant output circuit having afrequency of resonance an integral multiple above the resonant frequencyof the oscillator in which a damped wave train is produced, a secondnon-oscillating harmonic selector having an input circuit coupled to theoutput circuit of the first harmonic selector and a resonant outputcircuit having a frequency of resonance an integral multiple above thefrequency of resonance of the output circuit of the first harmonicselector, said second harmonic selector including means for rejectingpulses with amplitudes no greater than the second pulse of the dampedwave train in the output circuit of the first harmonic selector, and athird class C stage having a vacuum tube including an input circuitconnected between the grid and return electrode of the tube coupled tothe output circuit of the second class C stage, said third class C stagebeing provided with negative biasing means connected to the grid thereoffor rejecting pulses with amplitudes no greater than the second pulse ineach wave train appearing in the output circuit of the second class Cstage.

11. An electrical device comprising an oscillator having a fixedresonant frequency, a first non-oscillating clas C stage having a vacuumtube, said stage having an input circuit connected between the grid andreturn electrode of said vacuum tube coupled to the oscillator and anoutput circuit connected between the plate and return electrode of saidvacuum tube, including a tank circuit having a resonant frequency whichis an integral multiple above the resonant frequency of the oscillatorin which a damped wave train is produced, a second class C stage havinga vacuum tube, said stage having an input circuit connected between thegrid and return electrode of the vacuum tube in said second class Cstage, said input circuit being coupled to the output circuit of thefirst class C stage, said second class C stage having an output circuithaving a tank circuit with a frequency of resonance which is an integralmultiple of the resonant frequency of the tank circuit in the firststage, and said second class C stage including means to negatively biasthe grid of the vacuum tube to reject pulses with amplitudes no greaterthan the second pulse of the damped wave train in the output circuit ofthe first harmonic selector, a reactance tube circuit connected inparallel with the tank circuit of the second class C stage, analternating current generator connected to the reactance tube circuit toperiodically vary the frequency of the tank circuit in the second classC stage, and a third. class C stage having a vacuum tube including aninput circuit connected between the grid and return electrode of thetube coupled to the output circuit of the second class C stage, saidthird class C stage being provided with negative biasing means connectedto the grid thereof for rejecting pulses with amplitudes no greater thanthe second pulse in each wave train appearing in the output circuit ofthe second class C stage.

12. An electrical device comprising an oscillator, a firstnon-oscillating harmonic selector having an input circuit coupled to theoscillator and a resonant output circuit having a frequency of resonancean integral multiple above the resonant frequency of the oscillator inwhich a damped wave train is produced, a second nonoscillating harmonicselector having an input circuit coupled to the output circuit of thefirst harmonic selector and a resonant output circuit, said secondharmonic selector including means for rejecting a portion of each wavetrain impressed thereon to form a hiatus between suc- 'c essive wavetrains, and means to sweep the resonant frequency of the output circuitof the second harmonic selector.

References Cited in the file of this patent

